Three-dimensional fiber networks are known. These are generally derived from textile fabrics that have been impregnated with a thermoset polymer or a low melting thermoplastic and then molded so that the fabric has an array of projections rising from the plane of the fabric. For example, U.S. Pat. No. 4,631,221 describes a laminate containing a rigid three-dimensional fiber network having regularly arranged projections. The three-dimensional network is placed between two sheets of rigid material. The three-dimensional network used in the laminate is made by the deep-drawing of a sheet-like textile fabric to make projections. The textile fabric is impregnated with a thermoset resin and dried to yield a pre-preg prior to deep drawing, and is cured after deep-drawing. The textile fabric is made from a multifilament yarn so that a larger amount of resin can be absorbed into the interfilament regions.
U.S. Pat. No. 5,364,686 describes a three-dimensional shaped material which is made from a fabric comprising a yarn that has thermoplastic fibers mixed with higher melting reinforcing fibers; the fabric is shaped by deep drawing at a temperature high enough to melt the lower melting thermoplastic material but not the reinforcing fiber to yield a three-dimensional structure which becomes rigid after it is cooled, possibly due in part to the fixing of fiber crossover points. This also can be laminated so that it has rigid layers on the outside.
U.S. Pat. No. 4,890,877 describes an energy absorbing structure for use in automobile doors, wherein the energy absorbing structure is a highly stretchable lightweight material that has been coated with a resin (e.g. a thermoset) and then molded so that it has a series of projections, which are preferably truncated cones. The structure after molding does not appear to have an open fiber network appearance. U.S. Pat. No. 5,158,821 describes a fabric that can be easily deep drawn and then impregnated with a resin to make materials like those described above.
Thermoplastic three-dimensional fiber networks which are similar in appearance to those described above but which are much more resilient are described in commonly assigned copending U.S. application No. 08/577,65 now U.S. Pat. No. 5,791,062 to kim et al. These fiber networks are made from large diameter thermoplastic fibers, usually monofils, and have projections in which the fibers are not bonded to one another at the points where the fibers intersect one another. These fiber networks were not used in laminated products.
U.S. Pat. Nos. 4,584,228; 4,252,590; and Re 31,345 all describe non-woven matting materials that have undulating patterns of projections both above and below the plane of the fabric. These have impact absorbing properties. Finally, U.S. Pat. No. 4,472,472 describes protective devices in which impact is absorbed by bowed plastic members, which flex on impact but then recover afterwards to absorb future shocks.
The fiber network structures described above and elsewhere that are in sandwich structures generally are rigid and are intended for use mainly as lightweight structural materials. Sandwich structures that are resilient and can perform as cushioning or impact-absorbing materials are generally not known and have apparently not been described or even suggested. Such materials may be useful in a variety of applications.